A film having a gas barrier property (gas barrier film) as a kind of functional film has widely been put to practical use in the fields of food, medicine, agricultural chemicals, cosmetics, etc., wherein contents to be contained therein are stored or protected while the "quality" of the contents is liable to cause a problem. One of such important uses of the film includes a field of "packaging".
Packaging, i.e., making or putting an object into a package or wrap, or the material for the packaging is desired to have a wide variety of functions. For example, such functions of packaging may include: mechanical protective property, safety, sanitary property, workability, adaptability to goods (transparency, printability, heat sealing property), utility, profitability, etc. Among these functions, a "gas barrier property" to various gases, as one of the factors in the above-mentioned storability or protective property, is an important property for affecting the storability of the above contents such as food. Along with recent diversification in the form of goods distribution or in packaging technique, intensification of additive control, change in taste, etc., the importance of the gas barrier property has been increased more and more. On the other hand, the gas barrier property has heretofore been a serious weak point of ordinary plastic materials.
Factors which can deteriorate a food include oxygen, light, heat and/or moisture. Among these factors, oxygen has been considered to be a substance causing such deterioration. A material having a gas barrier property (gas barrier material) is a material which has a main function of effectively intercepting oxygen. Such a gas barrier material exhibits the function of intercepting oxygen, and simultaneously exhibits a function which is essential for various measures for controlling the deterioration of food (such as gas charging and vacuum packaging). The gas barrier material has been utilized very effectively in many fields such as food packaging inclusive of confectionery bags, bags for dried bonito, pouches for retorted foods, containers for carbonated drinks, etc., or packaging for cosmetics, agricultural chemicals, and medical use, on the basis of its barrier function to various kinds of gases such as oxygen, organic solvent vapors, aromas; or on the basis of its function of preventing corrosion, odor, sublimation, etc., based on the barrier function thereof.
Among films comprising a thermoplastic resin, those films comprising oriented polypropylene, polyester, polyamide, etc., particularly have excellent mechanical property, heat resistance, transparency, etc., and therefore these films are widely used as a packaging material. However, in a case where a film comprising such a material is used for food packaging, since the barrier property thereof to a gas such as oxygen is insufficient, the food as the contents in the package is liable to be deteriorated due to degradation based on oxidation, or the function of aerobic bacteria, etc. Furthermore, in such a case, an aroma component of the food permeates the package to be diffused to the outside of the package. As a result, there tend to occur various problems such that the flavor of the food is lost, or the contents are wetted with outside moisture due to the penetration of such moisture and the taste thereof becomes worse. Accordingly, when a film of the above-mentioned material such as polypropylene is used for food packaging, it is usual to adopt a method wherein another film (or layer) having an excellent gas barrier property is laminated onto the film of the above-mentioned material.
As a transparent plastic raw material having a small gas permeability (i.e., a large gas barrier property), there have heretofore been known some films comprising a raw material such as polyvinyl alcohol, polyethylene-vinyl alcohol copolymer, and polyvinylidene chloride-type resin. However, these plastic materials have an oxygen permeability to a certain degree which is never negligible, while a metal or glass raw material to be used for canned foods or bottled foods only has a substantially no oxygen permeability.
As a method of imparting a gas barrier property or increasing the gas barrier property of a resin, there has been known some methods. For example, Japanese Laid-Open Patent Application (KOKAI) No. 30944/1991 (i.e., Hei 3-30944) describes a process for producing a coated film wherein a coating composition comprising polyvinyl alcohol and synthetic hectorite in a wt. ratio of 20:80 is applied onto a biaxially oriented polyethylene terephthalate (OPET), and then dried.
However, such films provided by the above-mentioned conventional techniques still do not have a sufficient gas barrier property, and is not a satisfactory film having a gas barrier property suitable for practical use.
An object of the present invention is to provide a resin composition, a laminate, or a laminate film which has solved the above-mentioned problems.
A more specific object of the present invention is to provide a resin composition, a laminate, or a laminate film having a gas barrier property at a good level.